defmodule Rolodex do
  @moduledoc """
  Rolodex generates documentation for your Phoenix API.

  Rolodex inspects a Phoenix Router and transforms the `@doc` annotations on your
  controller actions into documentation data in the format of your choosing.

  `Rolodex.run/1` encapsulates the full documentation generation process. When
  invoked, it will:

  1) Traverse your Phoenix Router
  2) Collect documentation data for the API endpoints exposed by your router
  3) Serialize the data into a format of your choosing (e.g. Swagger JSON)
  4) Write the serialized data out to a destination of your choosing.

  Rolodex can be configured in the `config/` files for your Phoenix project. See
  `Rolodex.Config` for more details on configuration options.

  ## Features and resources

  - **Reusable parameter schemas** - See `Rolodex.Schema` for details on how to
  write reusable schemas for request and response parameters in your API.
  - **Structured annotations** - See `Rolodex.Route` for details on how to format
  annotations on your API route action functions for the Rolodex parser to handle
  - **Generic serialization** - The `Rolodex.Processor` behaviour encapsulates
  the basic steps needed to serialize API metadata into documentation. Rolodex
  ships with a valid Swagger JSON processor (see: `Rolodex.Processors.Swagger`)
  - **Generic writing** - The `Rolodex.Writer` behaviour encapsulates the basic
  steps needed to write out formatted docs. Rolodex ships with a file writer (
  see: `Rolodex.Writers.FileWriter`)

  ## High level example

      # Your Phoenix router
      defmodule MyRouter do
        pipeline :api do
          plug MyPlug
        end

        scope "/api" do
          pipe_through [:api]

          get "/test", MyController, :index
        end
      end

      # Your controller
      defmodule MyController do
        @doc [
          headers: ["X-Request-ID": uuid],
          body: [id: :uuid],
          query_params: [include: :string],
          path_params: [user_id: :uuid],
          responses: %{200 => MyResponse},
          metadata: [public: true],
          tags: ["foo", "bar"]
        ]
        @doc "My index action"
        def index(conn, _), do: conn
      end

      # Your response schema
      defmodule MyResponse do
        use Rolodex.Schema

        schema "MyResponse", desc: "A response" do
          field :id, :uuid
          field :name, :string, desc: "The response name"
        end
      end

      # In mix.exs
      config :rolodex,
        title: "MyApp",
        description: "An example",
        version: "1.0.0",
        router: MyRouter,
        pipelines: [
          api: [
            headers: ["Include-Meta": :boolean]
          ]
        ]

      # Then...
      Application.get_all_env(:rolodex)
      |> Rolodex.Config.new()
      |> Rolodex.run()

      # The JSON written out to file should look like
      %{
        "openapi" => "3.0.0",
        "info" => %{
          "title" => "MyApp",
          "description" => "An example",
          "version" => "1.0.0"
        },
        "paths" => %{
          "/api/test" => %{
            "get" => %{
              "metadata" => %{"public" => true},
              "parameters" => [
                %{
                  "in" => "header",
                  "name" => "X-Request-ID",
                  "schema" => %{
                    "type" => "string",
                    "format" => "uuid"
                  }
                },
                %{
                  "in" => "path",
                  "name" => "user_id",
                  "schema" => %{
                    "type" => "string",
                    "format" => "uuid"
                  }
                },
                %{
                  "in" => "query",
                  "name" => "include",
                  "schema" => %{
                    "type" => "string"
                  }
                }
              ],
              "responses" => %{
                "200" => %{
                  "content" => %{
                    "application/json" => %{
                      "schema" => %{
                        "ref" => "#/components/schemas/MyResponse"
                      }
                    }
                  }
                }
              },
              "requestBody" => %{
                "type" => "object",
                "properties" => %{
                  "id" => %{"type" => "string", "format" => "uuid"}
                }
              },
              "tags" => ["foo", "bar"]
            }
          }
        },
        "components" => %{
          "schemas" => %{
            "MyResponse" => %{
              "type" => "object",
              "description" => "A response",
              "properties" => %{
                "id" => %{"type" => "string", "format" => "uuid"},
                "name" => %{"type" => "string", "description" => "The response name"}
              }
            }
          }
        }
      }
  """

  alias Rolodex.{
    Config,
    Route,
    Schema
  }

  @route_fields_with_schemas [:body, :headers, :path_params, :query_params, :responses]

  @doc """
  Runs Rolodex and writes out documentation to the specified destination
  """
  @spec run(Rolodex.Config.t()) :: :ok | {:error, any()}
  def run(config) do
    generate_documentation(config)
    |> write(config)
  end

  defp write(processed, %Config{writer: writer} = config) do
    writer = Map.get(writer, :module)

    with {:ok, device} <- writer.init(config),
         :ok <- writer.write(device, processed),
         :ok <- writer.close(device) do
      :ok
    else
      err ->
        IO.puts("Failed to write docs with error:")
        IO.inspect(err)
    end
  end

  @doc """
  Generates a list of route docs and a map of response schemas. Passes both into
  the configured processor to generate the documentation JSON to be written to
  file.
  """
  @spec generate_documentation(Rolodex.Config.t()) :: String.t()
  def generate_documentation(%Config{processor: processor} = config) do
    routes = generate_routes(config)
    schemas = generate_schemas(routes)
    processor.process(config, routes, schemas)
  end

  @doc """
  Inspects the Phoenix Router provided in your `Rolodex.Config`. Iterates
  through the list of routes to generate a `Rolodex.Route` for each. It will
  filter out any route(s) that match the filter(s) you provide in your config.
  """
  @spec generate_routes(Rolodex.Config.t()) :: [Rolodex.Route.t()]
  def generate_routes(%Config{router: router} = config) do
    router.__routes__()
    |> Flow.from_enumerable()
    |> Flow.map(&Route.new(&1, config))
    |> Flow.reject(&(&1 == nil || Route.matches_filter?(&1, config)))
    |> Enum.to_list()
  end

  @doc """
  Inspects the request and response parameter data for each `Rolodex.Route`.
  From these routes, it collects a unique list of `Rolodex.Schema` references,
  and serializes each via `Rolodex.Schema.to_map/1`. The serialized schemas will
  be passed along to a `Rolodex.Processor` behaviour.
  """
  @spec generate_schemas([Rolodex.Route.t()]) :: map()
  def generate_schemas(routes) do
    routes
    |> Flow.from_enumerable()
    |> Flow.reduce(fn -> %{} end, &schemas_for_route/2)
    |> Map.new()
  end

  defp schemas_for_route(route, schemas) do
    unserialized_refs_for_route(route, schemas)
    |> Enum.reduce(schemas, fn ref, acc ->
      Map.put(acc, ref, Schema.to_map(ref))
    end)
  end

  # Looks at the route fields where users can provide `Rolodex.Schema` refs
  # that it now needs to serialize. Performs a DFS on each field to collect any
  # unserialized schema refs. We look at both the refs in the maps of data, PLUS
  # refs nested within the schemas themselves. We recursively traverse this graph
  # until we've collected all unseen refs for the current context.
  defp unserialized_refs_for_route(route, schemas) do
    # List of already serialized Rolodex.Schema refs in the route
    serialized_refs = Map.keys(schemas)

    route
    |> Map.take(@route_fields_with_schemas)
    |> Enum.reduce(MapSet.new(), fn {_, field}, acc ->
      collect_unserialized_refs(field, acc, serialized_refs)
    end)
    |> Enum.to_list()
  end

  defp collect_unserialized_refs(field, result, serialized_refs) when is_map(field) do
    field
    |> Schema.get_refs()
    |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))
  end

  defp collect_unserialized_refs(ref, result, serialized_refs) when is_atom(ref) do
    case Schema.is_schema_module?(ref) do
      true ->
        ref
        |> Schema.get_refs()
        |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))

      false ->
        result
    end
  end

  defp collect_unserialized_refs(_, acc, _), do: acc

  # If the current schema ref is unserialized, add to the MapSet of unserialized
  # refs, and then continue the recursive traversal
  defp collect_ref(ref, result, serialized_refs) do
    seen_refs = Enum.to_list(result) ++ serialized_refs

    case ref in seen_refs do
      true ->
        result

      false ->
        result = MapSet.put(result, ref)
        collect_unserialized_refs(ref, result, serialized_refs)
    end
  end
end